A resistance furnace generates heat by passing electrical energy through a resistance element. The resistance element is typically of high resistance, so as to produce a large amount of heat when electrical energy is flowing through it. Resistance furnaces are often used in metal smelting.
One type of power supply often used for a resistance furnace provides energy to the resistance element in the form of a series of power pulses. Each pulse carries a quantum of energy which maintains a constant amplitude current for a fixed period, at a given load resistance and line voltage. This type of power supply has a number of advantages over other types, such as: better accuracy of control, lower cost, low harmonic distortion on the power line, and the fact that the energy to the furnace may be isolated from the control equipment, thus minimizing the risk of endangering the operator. The power to the furnace can be controlled by varying the frequency of the pulses.
One object of the present invention is to provide a power supply for a resistance furnace which provides a novel way of controlling the frequency of pulses to the resistance element.
Another object of the present invention is to provide a power supply for a resistance furnace in which the frequency of pulses in controlled by external parameters such as load voltage and current, element temperature, and furnace temperature.
Other objects will appear hereinafter.